package com.momo.theta.sharding.util.snowflake;

/**
 * 雪花实例
 */
public class SnowFlake {

  /**
   * 起始的时间戳
   */
  private final static long START_STMP = 1480166465631L;
  /**
   * 每一部分占用的位数
   */
  private final static long SEQUENCE_BIT = 12; //序列号占用的位数
  private final static long MACHINE_BIT = 5;   //机器标识占用的位数
  private final static long DATACENTER_BIT = 5;//数据中心占用的位数
  /**
   * 每一部分的最大值
   */
  private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
  private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
  private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);
  /**
   * 每一部分向左的位移
   */
  private final static long MACHINE_LEFT = SEQUENCE_BIT;
  private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
  private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;
  private static SnowFlake instace;
  private long datacenterId;  //数据中心
  private long machineId;     //机器标识
  private long sequence = 0L; //序列号
  private long lastStmp = -1L;//上一次时间戳
  private SnowFlake(long datacenterId, long machineId) {
    if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
      throw new IllegalArgumentException(
          "datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
    }
    if (machineId > MAX_MACHINE_NUM || machineId < 0) {
      throw new IllegalArgumentException(
          "machineId can't be greater than MAX_MACHINE_NUM or less than 0");
    }
    this.datacenterId = datacenterId;
    this.machineId = machineId;
  }

  /**
   * 单子模式创建一个雪花实例
   *
   * @param datacenterId
   * @param machineId
   * @return
   */
  public static SnowFlake getSnowFlake(long datacenterId, long machineId) {
    if (instace == null) {
      instace = new SnowFlake(datacenterId, machineId);
    }

    return instace;
  }

  public static void main(String[] args) {
    SnowFlake snowFlake = new SnowFlake(2, 3);

    for (int i = 0; i < (1 << 12); i++) {
      System.out.println(snowFlake.nextId());
    }

  }

  /**
   * 产生下一个ID
   *
   * @return
   */
  public synchronized long nextId() {
    long currStmp = getNewstmp();
    if (currStmp < lastStmp) {
      throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
    }

    if (currStmp == lastStmp) {
      //相同毫秒内，序列号自增
      sequence = (sequence + 1) & MAX_SEQUENCE;
      //同一毫秒的序列数已经达到最大
      if (sequence == 0L) {
        currStmp = getNextMill();
      }
    } else {
      //不同毫秒内，序列号置为0
      sequence = 0L;
    }

    lastStmp = currStmp;

    return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
        | datacenterId << DATACENTER_LEFT       //数据中心部分
        | machineId << MACHINE_LEFT             //机器标识部分
        | sequence;                             //序列号部分
  }

  private long getNextMill() {
    long mill = getNewstmp();
    while (mill <= lastStmp) {
      mill = getNewstmp();
    }
    return mill;
  }

  private long getNewstmp() {
    return System.currentTimeMillis();
  }
}